Device for the metallisation of printed forms which are equipped with electrically conductive tracks and associated metallisation method

ABSTRACT

The invention relates to a printed circuit which is equipped with electrically conductive tracks and which can be obtained by means of gravure printing. Gravure printing can be used to obtain conductive tracks of a very small thickness, such that said tracks have a high electrical resistance. In order to reduce the electrical resistance of the tracks ( 30 ) thus obtained, the invention consists in connecting at least two first electrodes ( 9, 8 ) to opposite portions ( 17, 18 ) of the same track while the middle ( 19 ) of said track is immersed in an electrolytic bath ( 7 ). Moreover, the bath is connected to a second electrode ( 26 ) which is in turn connected to a second potential ( 15 ) having an opposite polarity to that of a first potential ( 14 ) connecting the first electrodes.

The invention concerns a metallization device for printed forms whichare equipped with electrically conductive tracks and an associatedmetallization method. The invention more particularly concerns ametallization device for a succession of patterns of electricallyconductive tracks having a low electrical conductivity and printed on adielectric support. In one example, the pattern particularly representsa planar antenna. The invention also concerns the field of printedcircuits obtained by any technique for printing electrically conductivetracks, such as, for example, by a heliogravure technique, offsetprinting, serigraphy, etc.

In document EP-A-0839,667, D1, a process is known for printing withelectrically conductive ink or the heliogravure printing technique. Thisprinting technique uses an engraved cylinder and a counter-pressurecylinder between which a thin dielectric support is placed in order tobe printed. The engraved cylinder is designed to be partially immersedin a vat containing an electrically-conductive ink while rotating aroundan axis of rotation of this same cylinder. The counter-pressure cylinderis designed to press the dielectric support onto the engraved cylinderwhile also rotating around another axis of rotation of this cylinder.The engraved cylinder and the counter-pressure cylinder are designed tocooperate such that the engraved cylinder prints electrically-conductiveink tracks onto the dielectric support.

This heliogravure printing technique is particularly interesting sinceit permits obtaining precise conductive tracks. The heliogravureprinting technique also permits obtaining conductive tracks of verysmall thickness (of the order of 1 μm, for example). The tracks obtainedby the heliogravure printing technique nevertheless have a highelectrical resistance.

Document U.S. Pat. No. 4,119,516, D2 describes an electrolytic devicepermitting metal to be deposited on the different conductive tracks byan electrolytic technique. This device can be used after the printedcircuit has been printed with conductive tracks. The electrolyticdevice, which is described in document D2, has a cathode and a pair ofanodes, the cathode being designed to be in contact with the conductivetracks and the pair of anodes being designed to be immersed in anelectrolytic vat containing an electrolytic bath. The cathode isconnected to a negative potential and the anode pair is connected to apositive potential, by means of a direct current voltage generator, todeposit the electrolytic metal onto the conductive tracks.

However, this metallization technique has the disadvantage of obtaininga metallization that is disrupted by a low electrical conductivity ofthe printed conductive tracks obtained by the previously-mentionedprinting techniques. The consequence of this is a poor distribution ofmetal thicknesses deposited on the tracks. Sometimes, the metallizationprocess can even be stopped.

As a result, the metallized printed circuits obtained by thismetallization technique cannot be sufficiently functional, and this isincompatible with an efficacious transmission or detection ofelectromagnetic signals from or by the printed circuit relative to anintegrated circuit of a smart card or an electronic tag, for example.

In order to resolve this problem while keeping the same printingtechniques for electrically conductive tracks, notably a heliogravureprinting technique, the invention provides a device for metallization inwhich at least two first electrodes connected to a first potential arepositioned at two opposite track sections with the same pattern, andsaid pattern is designed to be partially immersed in an electrolyticbath between these two first electrodes. These two first electrodes aremade in such a way that they are separated from one another by adistance less than or equal to one dimension of a pattern, whichdimension is measured relative to the direction of movement of thesupport in the bath. More precisely, the two first electrodes areseparated from one another by a distance less than or equal to a lengthof a pattern measured along the support between the two first electrodeswith regard to the direction of movement of the support in the bath. Thepositioning of these two first electrodes with regard to one anotherpermits assuring a metallization of all the tracks of the same patternby putting these same tracks at equipotential by means of these firstelectrodes in contact with the pattern. These two first electrodes areconnected to a first potential with a polarity that is opposite to asecond potential, which second potential is connected to a secondelectrode designed to supply the electrolytic bath with the secondpotential.

The subject of the invention is a metallization device for a dielectricsupport coated with patterns of electrically conductive tracks, andcomprising

an electrolytic station,

this electrolytic station comprises an electrolytic bath, firstelectrodes connected to a source of a first electrical potential with apolarity opposite to that of the second electrical potential, the bathbeing subjected to the second electrical potential by one or more secondelectrodes of the electrolytic station, characterized in that

the dielectric support is immersed in the electrolytic bath so that thetracks of the same pattern are connected in short-circuit to the firstpotential and to the second potential, and

at least two first electrodes are connected to opposite pattern sectionsof the same pattern while the middle section of this same pattern isimmersed in the bath.

The subject of the invention is also a metallization method for adielectric support coated with patterns of electrically conductivetracks, characterized in that

a—at least one conductive track pattern is subjected to an electrolyticbath by immersing the dielectric support in this bath, and by connectingthe tracks in short-circuit to a source of a first electrical potentialwith a polarity opposite that of a second potential to which theelectrolytic bath is subjected, and

b—opposite pattern sections of the same pattern are subjected to thefirst potential by means of at least two electrodes, while a middlesection of the pattern is immersed in the bath.

The invention will be better understood upon reading the descriptionthat follows and examining the figures that accompany it. These figuresare only shown by way of indication and do not at all limit theinvention. The figures show:

FIG. 1: A schematic diagram of a metallization device according to theinvention,

FIG. 2: A schematic diagram of a dielectric support according to theinvention,

FIG. 3: A schematic diagram of a variant of embodiment of themetallization device according to the invention,

FIG. 1 shows a metallization device 1 for a dielectric support 2,according to the invention. Dielectric support 2 can be, for example, adielectric substrate manufactured of PET, PVC, polycarbonate, ABS,impregnated or non-impregnated paper, epoxy glass, polyimide, LCP, etc.This dielectric support 2 is formed by elements 3 (see FIG. 2), eachcoated with a pattern 4 of electrically conductive tracks. Each of thepatterns can be connected together by means of at least one linkingtrack such as 37. Pattern 4 of the conductive tracks can represent aplanar antenna, as shown in FIG. 2, or a printed circuit of any otherform. A planar antenna can be integrated in a simple manner in smartcards or electronic tags, being connected with the integrated circuit bythe usual processes, such as wire soldering, flip-chip mounting or thelike. A planar antenna, as shown in FIG. 2, is formed by a succession ofconcentric whorls, each of the whorls forming an electrically conductivetrack 30.

The pattern of conductive tracks can be obtained by a heliogravureprinting technique using a gravure printing station 5, FIG. 1. Or thepattern of the conductive tracks can be obtained by other techniquessuch as, for example, serigraphy or offset printing techniques, such aspreviously mentioned. In one example, the heliogravure printingtechnique permits obtaining a track 1 μm thick, therefore very thin andallowing a high track density.

According to the invention, metallization device 1 comprises anelectrolytic station 6, and this station 6 can be placed downstream ofheliogravure printing station 5. This electrolytic station 6 comprisesan electrolyte bath 7 to bathe dielectric support 2. This electrolyticstation 6 also comprises first electrodes and at least one secondelectrode. In the preferred example of FIG. 1, the electrolytic stationcomprises five first electrodes 8, 9, 10, 11, 12, all connectedtogether, and a second electrode 13. The first electrodes place thetracks in short-circuit and, by permitting these tracks to be connectedto a first electrical potential source 14, permit putting the tracks atequipotential. The second electrode permits subjecting electrolytic bath7 to a second electrical potential source 15. The differences betweenthe potentials are such that it can be said that the first electrodesare connected to the first potential 14 with a polarity opposite to thesecond electrical potential 15 connecting the second electrode. Thefirst potential and the second potential, for example, are produced by avoltage rectifier 16 or by a voltage generator.

Electrolytic bath 7 can preferably be formed by a formulation based oncopper sulfate in acid medium, or by any other solution that can releasemetals during electrolysis. The polarity of the first electrodes and thepolarity of the second electrode depend on the nature of the solutioncontained in the electrolytic bath. In the case of a solution formed bycopper sulfate, the first electrodes are connected to the firstpotential 14 of negative polarity so as to draw copper ions towardsthese first electrodes and therefore towards the tracks duringelectrolysis, while the second electrode is connected topositive-polarity potential 15. Thus, the first electrodes designed tobe in contact with the tracks permit these tracks then to form cathodesdesigned to attract the cations while the second electrode forms ananode designed to attract the anions.

The first electrodes are positioned here so that they are situatedoutside the bath. Then an electrolysis is conducted between two firstelectrodes and the electrolytic bath, followed by contact of at leastone first electrode 8 (or 9) onto pattern 4 of conductive tracks, andthen followed by the immersion of at least a part of this conductivetrack pattern in the bath 7.

The two first electrodes 8 and 9 are separated from one another for adistance less than or equal to a length 21 of a pattern 4, length 21being measured along the support or insulating sheet relative to thedirection of movement of the support, as shown by the arrow in FIGS. 1and 2. In particular, at least two first electrodes 8 and 9 areconnected to opposite pattern sections 17 and 18 of the same pattern 4,FIG. 2. A pattern 4 comprises a first pattern section 17 and a secondpattern section 18, each of the sections or ends being opposite oneanother. These two opposite sections are separated by an intermediate ormiddle pattern section 19. During movement of support 2, the firstsection 17 of pattern 4 is electrolyzed first by connection to electrode8 and immersed in bath 7 while the second section 18 of pattern 4 iselectrolyzed last. When section 18 is electrolyzed by means of electrode8, section 17 comes to be electrolyzed by electrode 9.

The metallization device also has a drive means 22 for sheet 2 and asuccession of bath sections which sheet 2 goes in and out of. Thissuccession of bath sections permits improving the deposition of metalonto the tracks in conjunction with the movement of the pattern in thebath.

According to a first preferred embodiment of the invention shown by FIG.1, drive means 22 can be formed by a series of first rollers such as 8to 11 situated outside the bath, and by a series of second rollers 26situated in the bath. In the example of FIG. 1, the drive means isformed by four second rollers such as 26. In this preferred embodimentof the invention, the first rollers are metal and form first electrodes8, 9, 10, 11 and 12. The second rollers are preferably insulating andassure the immersion of the sheet between at least two first electrodesduring movement of the sheet. All of these rollers can be supported bythe same crossbar (not shown). Sheet 2 is driven by successive passagesfrom a first roller to a second roller and so on. These successivepassages from a first roller to a second roller and so on permitimproving the metal deposition on the tracks as the support moves in theelectrolytic bath. If the sheet is subjected to a tension that is toohigh and that might deform it, these rollers can be mounted on bearingsand/or motorized so as to reduce the tension between each of therollers.

In a variant of this, the drive means could comprise a first series offirst rollers 8, 9, 10, 11, 12 and a second series of first rollers 27mounted in correspondence and supported against the rollers of the firstseries of first rollers. The first series of first rollers correspondsto the first rollers previously described while the second series offirst rollers is shown by the dashed circles in FIG. 1. These two seriesof first rollers would permit a first face 24 and/or a second face 25 ofprinted insulating sheet 2 to be subjected to electrolysis, the firstface and the second face each being coated with at least one pattern ofelectrically conductive tracks. The first series of first rollers wouldbe positioned in such a way that first face 24 would be in contact withthese first rollers and the second series of first rollers would be madeup in such a way that second face 25 would be in contact with theselatter first rollers.

The first rollers are supplied with first potential 14 and the secondrollers are preferably insulating. The second rollers can also besupplied with the first potential as shown by the dashed line in FIG. 1.It would then suffice to regularly replace these second rollers, which,during electrolysis, could become progressively covered with metal.

In order to drive the sheet, the rollers are motorized. Nevertheless,only a few rollers need be motorized for the sheet to move sufficiently.The rate of rotation of the rollers is regulated so that the totalpassage duration is sufficient to form the desired thickness.

The metallization process of insulating sheet 2 in view of obtaining adielectric support printed with patterns of electrically conductivetracks is obtained by carrying out the following steps. First of all,patterns of conductive tracks, interconnected or not, are printed ontothe sheet by the heliogravure printing technique. In order to do this,heliogravure printing station 5, as previously mentioned, comprises anengraved cylinder 31 and a counter-pressure cylinder 32. Engravedcylinder 31 comprises openings 33 designed to print the conductivetracks onto support 2. The engraved cylinder and the counter-pressurecylinder are supported against one another with the dielectric supportin between. The engraved cylinder and the counter-pressure cylinderrotate around their respective axes, while permitting obtaining aprecise printing of tracks onto the insulating sheet. A scraper 34 isprovided to obtain a precise printing of tracks onto the dielectricsupport. Scraper 34 then permits removing the excess ink situatedoutside the openings of the engraved cylinder before thecounter-pressure cylinder prints the pattern of conductive tracks ontothe support pressed by the counter-pressure cylinder.

Once printed, the conductive tracks are then subjected to electrolytebath 7 by immersing the dielectric support in this bath connected to thesecond electrical potential of positive polarity, and by connecting thetracks in short-circuit to the first electrical potential source ofnegative polarity. The continuity of electrolysis on the same pattern isassured during movement of the sheet between the rollers by means of aprevious calibration of the distance between at least two first rollerscorresponding to two first electrodes, which distance between these twofirst rollers is such that it corresponds to a length less than or equalto a length 21 of a pattern 4 of the support measured along sheet 2relative to the direction of movement of the support in the bath.

The rollers forming the first electrodes are also made so that theycomprise a length measured relative to a direction perpendicular to thedirection of movement of the support in the bath at least equal to awidth 38 of a pattern 4, which width of a pattern 4 is measured on thesupport relative to the same direction perpendicular to the direction ofmovement of the support in the bath. More precisely, the first rollersor first electrodes comprise a length permitting covering all the tracksof at least the same pattern 4 relative to a direction perpendicular tothe direction of movement of the support in the bath. The first rollersor first electrodes could comprise a length dependent on the number ofpatterns present on support 2.

In the example, the electrolysis steps are repeated as many times asthere are elements 3 immersed in station 6, in particular because thedistance between the first rollers 8 and 9, or 9 and 10, or 10 and 11,or 11 and 12, measured along support 2, is less than or equal to thedimension of a pattern 4.

According to the preferred embodiment of the invention of FIG. 1, thesteps are repeated in the same electrolytic bath since rollers such as26 are immersed in the same bath.

As a variant, it is possible to use a series of compartments 28, eachcomprising an electrolytic bath, FIG. 4. In this example, themetallization device according to this variant has a series of threecompartments, such as 28. These compartments are created in such a waythat they permit the passage of dielectric support 2 through a slot.Each compartment, according to the invention, has a dimension less thana pattern 4. Tracks 30 of each support element are connected to at leasttwo first cylindrical electrodes 29 and 35. These first electrodes 29and 35 are in contact with each of the tracks by blocks situated outsidecompartment 28. In one example, the blocks can be replaced by rollers.Electrodes 29 and 35 connected to each other are in contact withsections 18 and 17, respectively. A similar mounting is adapted for theother compartments. Contact with the bath is assured by an electrode 36during passage of the support into each compartment.

A sensor C of the level of the electrolytic bath can be positioned so asto prevent a possible lowering of the level that could impede correctelectrolysis of patterns 4, FIG. 1.

Printing step 5 and electrolysis step 6 that permit ending up at thecorrect metallization are preferably performed one after the otherwithout stopping in between, so as to prevent detachments of print thatcould result infallibly from an intermediate wrapping up. The movementspeed of the sheet during the printing step can be different from themovement speed of the sheet during the electrolysis step; an adapter 39for the movement speed of the sheet could be provided, which adapter canbe placed between the heliogravure printing station 5 and electrolyticstation 6, as shown very schematically in FIG. 1. In one example, themovement speed of the sheet during the step of printing by heliogravureis 50 to 100 meters per minute and the movement speed of the sheetduring the electrolysis step is 1 to 10 meters per minute.

In practice, electrolysis step 6 that permits arriving at the correctmetallization is conducted at rates comprised between 1 and 10 metersper minute.

1. A metallization device for a dielectric support coated with patternsof electrically conductive tracks, and comprising an electrolyticstation, this electrolytic station comprises an electrolytic bath, firstelectrodes connected to a source of a first electrical potential, with apolarity opposite to that of a second electrical potential, the bathbeing subjected to the second electrical potential by one or more secondelectrodes of the electrolytic station, characterized in that thedielectric support is immersed in the electrolytic bath so that thetracks of the same pattern are connected in short-circuit to the firstpotential and to the second potential, and at least two first electrodesare connected to opposite pattern sections of the same pattern while themiddle section of this same pattern is immersed in the bath.
 2. Thedevice according to claim 1, further characterized in that two firstelectrodes are separated from one another by a distance less than alength of a pattern measured along the support relative to the directionof movement of the support in the bath.
 3. The device according to claim1, further characterized in that it comprises a drive means for thedielectric support, and a succession of bath sections into and out ofwhich the support is passed.
 4. The device according to claim 3, furthercharacterized in that it comprises a series of first rollers situatedoutside the bath, and a series of second rollers situated in the bath,the dielectric support passing alternatively from a first roller to asecond roller and so on, the first rollers being supplied at the firstpotential, the second rollers preferably being insulating.
 5. The deviceaccording to claim 4, further characterized in that the rollers aremotorized.
 6. The device according to claim 1, further characterized inthat the electrolytic bath is a formulation based on copper sulfate inacid medium.
 7. The device according to claim 1, further characterizedin that the dielectric support is positioned between a first series offirst electrodes and a second series of first electrodes.
 8. The deviceaccording to claim 1, further characterized in that each of thesepatterns are connected together by at least one connection track.
 9. Ametallization method for a dielectric support coated with patterns ofelectrically conductive tracks, characterized in that a—at least oneconductive track pattern is subjected to an electrolytic bath byimmersing the dielectric support in this bath, and by connecting thetracks in short-circuit to a source of a first electrical potential witha polarity opposite to that of a second potential to which theelectrolytic bath is subjected, and b—opposite pattern sections of thesame pattern are subjected to the first potential by means of at leasttwo electrodes, while a middle section of the pattern is immersed in thebath.
 10. The method according to claim 9, further characterized in thatsteps a and b are repeated.
 11. The method according to claim 10,further characterized in that for the repetition, the same bath is used.12. The method according to claim 9, further characterized in that theelectrolytic bath is a formulation based on copper sulfate in acidmedium.
 13. The method according to claim 9, further characterized inthat the steps a and b are successive in time at a rate comprisedbetween 1 to 10 meters per minute.